Systems and methods for detecting fake or altered bullion, coins, and metal

ABSTRACT

A system for verifying authenticity of precious metal coins and bars includes a sensor system defining a sample region configured to receive a precious metal coin or bar therein; a sample support; and a data processor configured to communicate with the sensor system so as to receive a detection signal therefrom and to provide an output signal. The system includes a data storage device and an output display. The sensor system detects a bulk electrical property of the coin or bar. The data processor processes the detection signal and retrieves a stored physical property from the data storage device to provide an output signal that includes at least a measured value of the bulk electrical property and a corresponding range of expected values. The output display uses the output signal to display information for a user to be able to make an authenticity verification of the coin or bar.

This application claims priority to U.S. Provisional Application No.62/280,028 filed Jan. 18, 2016, the entire content of which is herebyincorporated by reference.

BACKGROUND 1. Technical Field

The field of the currently claimed embodiments of this invention relatesto devices and methods for verifying the authenticity of precious metalcoins and bars.

2. Discussion of Related Art

Precious metal coins and bullion are valued by their metal content. Byaltering the metal, or by inserting a different metal into a coin orbar, a fake or altered bar or coin can be made to look, feel, and weighthe same as a real one. Even testing the surface of the coin or bar doesnot guarantee that the inside is actually made of the correct material.

No single method of precious metal sample determination can guaranteethat the sample is what it is supposed to be. Existing methods are slow,messy, and expensive, and some are destructive. For example, melting canbe used, but obviously this destroys the precious metal sample and isvery expensive.

Therefore, there remains a need for a detection device that is accurate,fast, portable, and non-destructive.

SUMMARY

According to some embodiments of the present invention, a system forverifying authenticity of precious metal coins and bars includes asensor system defining a sample region configured to receive at leastone of a precious metal coin or a precious metal bar therein. The systemincludes a sample support arranged to support the at least one of theprecious metal coin or the precious metal bar in the sample region. Thesystem includes a data processor configured to communicate with thesensor system so as to receive a detection signal therefrom and toprovide an output signal. The system includes a data storage deviceconfigured to communicate with the data processor, the data storagedevice storing at least some physical properties corresponding to aprecious metal of interest. The system also includes an output displayconfigured to communicate with the data processor to receive the outputsignal and to display information based on the output signal. The sensorsystem detects at least one of a bulk electrical property of the atleast one of the precious metal coin or the precious metal bar. The dataprocessor is configured to process the detection signal from the sensorsystem and to retrieve a stored physical property corresponding to aprecious metal from the data storage device to provide the output signalsuch that the output signal includes at least a measured value of thebulk electrical property and a corresponding range of expected values ofthe bulk electrical property. The output display uses the output signalto display information based on the measured value of the bulkelectrical property and the corresponding range of expected values ofthe bulk electrical property for a user to be able to make anauthenticity verification of the precious metal coin or the preciousmetal bar.

According to some embodiments of the present invention, a system forverifying authenticity of precious metal coins and bars includes asensor system defining a sample region configured to receive at leastone of a precious metal coin or a precious metal bar therein. The systemincludes a sample support arranged to support the at least one of theprecious metal coin or the precious metal bar in the sample region. Thesystem includes a data processor configured to communicate with thesensor system so as to receive a detection signal therefrom and toprovide an output signal. The system includes a data storage deviceconfigured to communicate with the data processor, the data storagedevice storing at least some physical properties corresponding to aprecious metal of interest. The system also includes an output displayconfigured to communicate with the data processor to receive the outputsignal and to display information based on the output signal. The sensorsystem detects a surface property of first and second sides of theprecious metal coin or the precious metal bar. The data processor isconfigured to process the detection signal from the sensor system toprovide the output signal such that the output signal includes at leasta measured value of a thickness value of the precious metal coin or theprecious metal bar. The output display uses the output signal to displayinformation based on the thickness value of the precious metal coin orthe precious metal bar for a user to be able to make an authenticityverification of the precious metal coin or the precious metal bar.

According to some embodiments of the invention, a method for verifyingauthenticity of precious metal coins and bars using an electronicapparatus includes inputting into the electronic apparatus informationidentifying at least a type of a precious metal coin or a precious metalbar to be verified. The method includes performing a measurement of abulk electrical property of the precious metal coin or the preciousmetal bar using the electronic apparatus. The method includes retrievinga stored bulk electrical property of the precious metal coin or theprecious metal bar corresponding to the measured bulk electricalproperty for the inputted type of the precious metal coin or theprecious metal bar. The method includes providing information from theelectronic apparatus for verification of authenticity of the preciousmetal coin or the precious metal bar based on the measured bulkelectrical property and the retrieved bulk electrical property.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objectives and advantages will become apparent from aconsideration of the description, drawings, and examples.

FIG. 1A is a first schematic drawing of a precious metal verificationsystem according to some embodiments of the present invention;

FIG. 1B is a second schematic drawing of a precious metal verificationsystem according to some additional embodiments of the presentinvention;

FIG. 1C is a third schematic drawing of a precious metal verificationsystem according to some additional embodiments of the presentinvention;

FIG. 1D is a fourth schematic drawing of a precious metal verificationsystem according to some additional embodiments of the presentinvention;

FIG. 2 shows the outside of the device according to some embodiments andgenerally illustrates how different features are related;

FIG. 3 shows a cross-section of the device illustrating how the weightsensor supports the first electrical coil, and where the supportstructure for the second electrical coil is located;

FIG. 4A illustrates a user interface for comparing an expected diameterof a sample to the actual diameter of the sample;

FIG. 4B illustrates a user interface for comparing an expected area of asample to the actual area of the sample;

FIG. 5 shows the an example display according to some embodiments;

FIG. 6 shows the overall circuit plan according to some embodiments;

FIG. 7 shows details of the analog circuit topology according to someembodiments;

FIG. 8 shows the internals of the field-programmable gate array (FPGA),and how the phase angles are measured off the analog/digital signalsaccording to some embodiments;

FIG. 9 shows schematically how the mechanical thickness of the sample ismeasured according to some embodiments; and

FIG. 10 shows how the electrical thickness is measured according to someembodiments.

DETAILED DESCRIPTION

Some embodiments of the current invention are discussed in detail below.In describing embodiments, specific terminology is employed for the sakeof clarity. However, the invention is not intended to be limited to thespecific terminology so selected. A person skilled in the relevant artwill recognize that other equivalent components can be employed andother methods developed without departing from the broad concepts of thecurrent invention. All references cited anywhere in this specification,including the Background and Detailed Description sections, areincorporated by reference as if each had been individually incorporated.

Precious metal coins and bullion are valued by their metal content. Theterm “bullion” refers to precious metal objects such as bars, coins,and/or rounds that are valued in terms of their metal content. The term“coins” is intended to include numismatic coins and bullion coins inwhich numismatic coins have value as a coin either as money and/or as acollectable item and bullion coins have value based primarily upon themetal content with a small premium. A precious metal “round” can beconsidered to be a type of coin in a general sense, as will be intendedherein. By altering the metal, or by inserting a different metal into acoin or bar, a fake or altered bar or coin can be made to look, feel,and weigh the same as a real one. Even testing the surface of the coinor bar does not guarantee that the inside of the bar is actually thecorrect material. The device and methods disclosed herein allow a userto look all the way through a bar or coin and determine whether themetal is the correct metal or alloy.

By measuring the thickness of the sample in two different ways, incombination with knowing the alloy or element, and the alloy orelement's resistivity, the resistivity through the entire sample isvalidated. Also, knowing the thickness and the weight in combinationwith the area of the coin or bullion sample gives the specific gravity,which for a given alloy is also known. If the resistivity through thebulk is correct, and the specific gravity is correct, then the metalelement or alloy must be the one represented by the coin or bullion.

The claimed invention differs from what currently exists. Using x-raybackscatter, the surface of a precious metal (PM) sample can be measuredfor elemental composition. However, only the surface is measured(typically 10 micro-inches deep), so plating can fool this method.Ultrasound can be used to find discontinuities in the bulk of a PMsample, but the method requires a mechanical thickness measurement, andindex matching fluids. Specific gravity can be measured by immersion ina fluid bath, but this method is messy.

None of these methods alone constitutes a certain measurement that thePM is correct and consistent through the bulk, so multiple measurementsare required for assurance. The systems and methods described herein canverify the authenticity of the PM sample through its bulk usingelectrical measurements, and no liquids are required.

The systems and methods according to some embodiments measure thethickness of the sample, which is not an easy dimension to measure, andallow the user to measure the diameter (in the case of coins) or thelength and width (in the case of bars) and easily determine the specificgravity without immersion in a liquid bath. In combination with the bulkresistivity, the PM sample is validated completely. The process is fastand the system is easy to use. The systems and methods do not modify thesample, and completely check the material through the bulk. They alsowork on thin and thick samples.

A system for verifying authenticity of precious metal coins and bars isrepresented schematically in FIG. 1A. The system 10 includes a sensorsystem 12 defining a sample region 14 configured to receive at least oneof a precious metal coin or a precious metal bar therein. The system 10further includes a sample support 16 arranged to support the at leastone of the precious metal coin or the precious metal bar in the sampleregion 14. The system 10 includes a data processor 18 configured tocommunicate with the sensor system 12 so as to receive a detectionsignal therefrom and to provide an output signal. The system 10 includesa data storage device 20 configured to communicate with the dataprocessor 18, the data storage device 20 storing at least some physicalproperties corresponding to a precious metal of interest. The system 10also includes an output display 22 configured to communicate with thedata processor 18 to receive the output signal and to displayinformation based on the output signal. The sensor system 12 detects atleast one of a bulk electrical property of the at least one of theprecious metal coin or the precious metal bar. The data processor 18 isconfigured to process the detection signal from the sensor system 12 andto retrieve a stored physical property corresponding to a precious metalfrom the data storage device 20 to provide the output signal such thatthe output signal includes at least a measured value of the bulkelectrical property and a corresponding range of expected values of thebulk electrical property. The output display 22 uses the output signalto display information based on the measured value of the bulkelectrical property and the corresponding range of expected values ofthe bulk electrical property for a user to be able to make anauthenticity verification of the precious metal coin or the preciousmetal bar.

According to some embodiments of the invention, the sensor system 12further detects a surface electrical property of the at least one of theprecious metal coin or the precious metal bar. The data processor 18 isfurther configured to process the detection signal from the sensorsystem 12 and to retrieve a stored physical property corresponding to aprecious metal from the data storage device 20 to provide the outputsignal such that the output signal includes at least the measured valueof surface electrical property and a corresponding range of expectedvalues of the surface electrical property. The output display 22 usesthe output signal to display information based on the measured value ofthe surface electrical property and the corresponding range of expectedvalues of the surface electrical property for a user to be able to makean authenticity verification of the precious metal coin or the preciousmetal bar.

According to some embodiments of the invention, the system 10 furtherincludes a user input system configured to communicate with the datastorage device 20 and the data processor 18. The user input systemallows a user to select at least one of a precious metal type, alloyparameters, weight, or shape.

According to some embodiments of the invention, the sensor system 12further detects a surface property of first and second sides of theprecious metal coin or the precious metal bar. The data processor 18 isconfigured to process the detection signal from the sensor system 12 toprovide the output signal such that the output signal includes at leasta measured value of a thickness value of the precious metal coin or theprecious metal bar. The output display 22 uses the output signal todisplay information based on the thickness value of the precious metalcoin or the precious metal bar for a user to be able to make anauthenticity verification of the precious metal coin or the preciousmetal bar.

According to some embodiments of the invention, the data processor 18 isfurther configured to retrieve a specific gravity corresponding to aprecious metal from the data storage device 20 and receive a weightvalue corresponding to the precious metal coin or the precious metalbar, and to provide the output signal such that the output signalfurther includes an expected diameter of the precious metal coin or anexpected area of the precious metal bar. The information based on thethickness value is the expected diameter of the precious metal coin oran expected length and width of the precious metal bar.

A system for verifying authenticity of precious metal coins and bars isrepresented schematically in FIG. 1B. The system 100 includes a signalgenerator 102, and a sample support 104 arranged proximate the signalgenerator 102, the sample support 104 having a sample region 106 tosupport at least one of a precious metal coin or a precious metal bar.The system 100 also includes a sensor system 108. The sensor system 108includes first and second electrical coils 110, 112 spaced apart withthe sample region 106 therebetween. The first and second electricalcoils 110, 112 are spaced apart sufficiently widely to accommodate theprecious metal coin or the precious metal bar therebetween. The sensorsystem 108 also includes a sensor circuit 114 selectively connecting thesignal generator 102 to the first and second electrical coils 110, 112.The sensor circuit 114 is configured to provide a measurement of acurrent in the first electrical coil 110 and a measurement of a voltageinduced in the second electrical coil 112.

The system 100 also includes a data processor 116. The data processor116 is configured to communicate with the sensor system 108 so as toreceive the measurement of the current through the first electrical coil110 and the measurement of the voltage induced in the second electricalcoil 112. The data processor 116 is configured to receive a surfaceresistivity value corresponding to the precious metal coin or theprecious metal bar. The data processor 116 is also configured to receivea thickness value of the precious metal coin or the precious metal bar.The data processor 116 is configured to calculate a bulk property of theprecious metal coin or the precious metal bar based on the measurementof the current and the measurement of the voltage. The data processor116 is configured to compare the bulk property to a test property basedon the surface resistivity value and the thickness value to determineone of agreement or disagreement therewith, and provide informationconcerning verification of authenticity of the precious metal coin orthe precious metal bar based on the agreement or disagreement betweenthe bulk property and the test property.

While the example above uses the measurement of the current through thefirst electrical coil 110 and the measurement of the voltage induced inthe second electrical coil 112 to calculate a bulk property of theprecious metal coin or the precious metal bar, an alternative would beto measure or control the voltage for the first electrical coil 110 andestimate the current drive based on impedance, and to measure thecurrent in the second electrical coil 112 and estimate the magnetic fluxfrom this current and the impedance.

According to some embodiments of the invention, the data processor 116is configured to calculate the bulk property based on a phase shiftbetween the measurement of the current and the measurement of thevoltage. According to some embodiments, the bulk property is a bulkresistivity of the precious metal coin or the precious metal bar.

According to some embodiments of the invention, the data processor 116is configured to control the signal generator 102 to adjust a frequencyof a voltage applied to the first electrical coil 110 such that a phaseshift between the measurement of the current and the measurement of thevoltage has a predetermined value. The data processor 116 is configuredto calculate the bulk property of the precious metal coin or theprecious metal bar based on the frequency at which the phase shift hasthe predetermined value and the indication of the thickness value of theprecious metal coin or the precious metal bar. According to someembodiments, the predetermined value of the phase shift is 45 degrees.

A system for verifying authenticity of precious metal coins and barsaccording to some embodiments is represented schematically in FIG. 1C,wherein like reference numerals as in FIG. 1B correspond to likefeatures. In addition to the features described with reference to FIG.1B, the system 100 according to some embodiments includes a sensorsystem 108 that further includes a second sensor circuit 118 selectivelyconnecting the signal generator 102 to the first electrical coil 110 toprovide a second measurement of a current in the first electrical coil110. The data processor 116 is configured to communicate with the sensorsystem 108 so as to receive the second measurement of the currentthrough the first electrical coil 110. The data processor 116 isconfigured to calculate the surface resistivity value of the preciousmetal coin or the precious metal bar based on the second measurement ofthe current through the first electrical coil 110. The data processor116 is configured to compare the bulk property to a test property basedon the calculated surface resistivity value and the thickness value todetermine one of agreement or disagreement therewith, and provideinformation concerning verification of authenticity of the preciousmetal coin or the precious metal bar based on the agreement ordisagreement between the bulk property and the test property.

According to some embodiments of the invention, the sensor system 108further includes a third sensor circuit 120 selectively connecting thesignal generator 102 to the second electrical coil 112 to provide ameasurement of a current in the second electrical coil 112. The dataprocessor 116 is configured to communicate with the sensor system 108 soas to receive the measurement of the current through the secondelectrical coil 112. The data processor 116 is configured to calculatethe thickness value based on the second measurement of the currentthrough the first electrical coil and the measurement of the currentthrough the second electrical coil. The data processor 116 is configuredto provide information concerning verification of authenticity of theprecious metal coin or the precious metal bar based on the calculatedthickness value.

According to some embodiments of the invention, the system furtherincludes a user interface in communication with the data processor. Theuser interface may include an input device and a display device. Anexample of an input device includes a keypad that includes one or moretouch-sensitive or depressible buttons. However, the broad concepts ofthe current invention are not limited to only this example. The displaydevice may be a visual display, such as a display screen or a lightsource, for example. The display device may also include an audio devicethat provides voice commands, beeps, or other sounds that enable thesystem to communicate with a user. The input device and output devicemay be combined in a touch-sensitive display. According to someembodiments, the system can include multiple input devices and displaydevices. An example input device and display device is shown in FIG. 2,described below.

According to some embodiments of the invention, the user interface isconfigured to receive an indication from a user of an expectedcomposition of precious metal coin or the precious metal bar. The dataprocessor according to some embodiments is configured to receive thesurface resistivity value corresponding to the precious metal coin orthe precious metal bar from a database based on the indication of theexpected composition received from the user. According to someembodiments, the user interface is configured to receive from a user thethickness value of the precious metal coin or the precious metal bar.

According to some embodiments of the invention, the user interface isconfigured to display information concerning verification ofauthenticity of the precious metal coin or the precious metal bar.According to some embodiments of the invention, the user interface isconfigured to display one of an expected length, width, or diameter ofthe sample via the display device. According to some embodiments, theuser interface is configured to display a non-numerical indication ofinformation concerning verification of authenticity of the preciousmetal coin or the precious metal bar. According to some embodiments, theuser is configured to display an indication of a difference between anexpected value of the precious metal coin or the precious metal bar anda value determined using the sensor system. The display may show amargin of error for an expected value, and may indicate whether thedetermined value falls within the margin. The display may indicate anacceptable margin by displaying a green region, and indicating whetherthe determined value falls within the green region. The display may useother colors, for example, yellow and red, to indicate margins of errorthat are questionable or are too high for the sample to be valid. If thedetermined value falls within the red region, for example, the sample islikely inauthentic.

According to some embodiments of the invention, the system 100 includesa second sensor circuit 118 selectively connecting the signal generator102 to the first electrical coil 110, the second sensor circuit beingconfigured to provide a second measurement of a current in the firstelectrical coil 110. The system 100 also includes a third sensor circuit120 selectively connecting the signal generator 102 to the secondelectrical coil 112, the third sensor circuit 120 being configured toprovide a measurement of a current in the second electrical coil 112.The data processor 116 is configured to communicate with the sensorsystem 108 so as to receive the second measurement of the currentthrough the first electrical coil 110 and the measurement of the currentthrough the second electrical coil 112, receive a specific gravity valuecorresponding to the precious metal coin or the precious metal bar, andreceive a weight value of the precious metal coin or the precious metalbar. The data processor 116 is configured to calculate a thickness valueof the precious metal coin or the precious metal bar based on the secondmeasurement of the current in the first electrical coil and themeasurement of the current in the second electrical coil, and calculatea value of a length or a diameter of the precious metal coin or theprecious metal bar based on the specific gravity value, the weightvalue, and the calculated thickness.

According to some embodiments of the invention, the data processor 116is further configured to determine a first distance between the firstelectrical coil 110 and the precious metal coin or the precious metalbar based on the second measurement of the current through the firstelectrical coil 110. The data processor 116 is further configured todetermine a second distance between the second electrical coil 112 andthe precious metal coin or the precious metal bar based on themeasurement of the current through the second electrical coil 112. Thedata processor 116 is configured to determine the thickness value of theprecious metal coin or the precious metal bar based on the firstdistance, the second distance, and a pre-determined distanced betweenthe first electrical coil 110 and the second electrical coil 112.

According to some embodiments of the invention, the data processor 116is configured to calculate an expected area of the sample based on thethickness, the specific gravity value, and the weight value. The userinterface is configured to provide a non-numerical indication of theexpected area and an acceptable error range to allow a user to comparethe expected area to an actual area of the precious metal coin or theprecious metal bar.

According to some embodiments of the invention, the user interface isconfigured to indicate first and second reference lines for positioningfirst and second edges of the precious metal bar. The user interface isalso configured to indicate third and fourth reference lines indicatingexpected positions of third and fourth edges of the precious metal barbased on the expected area. The user interface is configured to receiveinput from a user adjusting a position of one of the third and fourthreference lines to correspond to one of the third and fourth edges ofthe precious metal bar. The user interface is configured to adjust theother of the third and fourth reference lines to indicate the expectedposition of the other of the third and fourth edges of the preciousmetal bar based on the expected area, and indicate an acceptable errorrange to allow a user to compare the expected area of the precious metalbar to an actual area of the precious metal bar.

According to some embodiments of the invention, the system includes aweight measurement component in communication with the data processor.The data processor is configured to receive the weight value of theprecious metal coin or the precious metal bar from the weightmeasurement component.

A system 100 for verifying authenticity of precious metal coins and barsaccording to some embodiments is shown in FIG. 1D, wherein likereference numerals as in FIG. 1B indicate like features. The system 100includes a signal generator 102, and a sample support 104 arrangedproximate the signal generator 102. The sample support 104 has a sampleregion 106 to support at least one of a precious metal coin or aprecious metal bar. The system 100 includes a sensor system 108including first and second electrical coils 110, 112 spaced apart withthe sample region 106 therebetween. The first and second electricalcoils 110, 112 are spaced apart sufficiently widely to accommodate theprecious metal coin or the precious metal bar therebetween. The sensorsystem 108 includes a first sensor circuit 122 selectively connectingthe signal generator 102 to the first electrical coil 110. The firstsensor circuit 122 is configured to provide a measurement of a currentin the first electrical coil 110. The sensor system 108 includes asecond sensor circuit 124 selectively connecting the signal generator102 to the second electrical coil 112, the second sensor circuit 124being configured to provide a measurement of a current in the secondelectrical coil 112. The system 100 includes a data processor 116configured to communicate with the sensor system 108 so as to receivethe measurement of the current through the first electrical coil 110 andthe measurement of the current through the second electrical coil 112.The data processor 116 is configured to receive a specific gravity valuecorresponding to the precious metal coin or the precious metal bar, andreceive a weight value of the precious metal coin or the precious metalbar. The data processor 116 is configured to calculate a thickness valueof the precious metal coin or the precious metal bar based on themeasurement of the current in the first electrical coil and themeasurement of the current in the second electrical coil. The dataprocessor 116 is configured to calculate a value of a length or adiameter of the precious metal coin or the precious metal bar based onthe specific gravity value, the weight value, and the calculatedthickness.

According to some embodiments, the data processor 116 is furtherconfigured to determine a first distance between the first electricalcoil and the precious metal coin or the precious metal bar based on themeasurement of the current through the first electrical coil. The dataprocessor 116 is further configured to determine a second distancebetween the second electrical coil and the precious metal coin or theprecious metal bar based on the measurement of the current through thesecond electrical coil. The data processor 116 is further configured todetermine the thickness value of the precious metal coin or the preciousmetal bar based on the first distance, the second distance, and apre-determined distanced between the first electrical coil and thesecond electrical coil.

The system according to the embodiments of the invention may also bereferred to herein as a “detection system” or “detection device.” Thesignal generator may also be referred to herein as a “sine wavegenerator.”

According to some embodiments of the invention, a method for verifyingauthenticity of precious metal coins and bars includes inputting intothe electronic apparatus information identifying at least a type of aprecious metal coin or a precious metal bar to be verified. The methodfurther includes performing a measurement of a bulk electrical propertyof the precious metal coin or the precious metal bar using theelectronic apparatus. The method includes retrieving a stored bulkelectrical property of the precious metal coin or the precious metal barcorresponding to the measured bulk electrical property for the inputtedtype of the precious metal coin or the precious metal bar. The methodalso includes providing information from the electronic apparatus forverification of authenticity of the precious metal coin or the preciousmetal bar based on the measurement of the bulk electrical property andthe stored bulk electrical property.

According to some embodiments of the invention, the method furtherincludes performing a measurement of a surface electrical property ofthe precious metal coin or the precious metal bar using the electronicapparatus. The method further includes retrieving a stored surfaceelectrical property of the precious metal coin or the precious metal barcorresponding to the measured surface electrical property for theinputted type of the precious metal coin or the precious metal bar. Themethod also includes providing information from the electronic apparatusfor verification of authenticity of the precious metal coin or theprecious metal bar based on the measurement of the surface electricalproperty and the stored surface electrical property.

According to some embodiments of the invention, the method furtherincludes performing a measurement of a surface electrical property offirst and second sides of the precious metal coin or the precious metalbar using the electronic apparatus. The method includes calculating athickness of the sample based on the surface electrical property of thefirst and second sides of the precious metal coin or the precious metalbar using the electronic apparatus. The method further includesproviding information from the electronic apparatus for verification ofauthenticity of the precious metal coin or the precious metal bar basedon the measurement of the thickness of the precious metal coin or theprecious metal bar.

According to some embodiments of the invention, a method for verifyingauthenticity of precious metal coins and bars includes receiving asurface resistivity value corresponding to the precious metal coin orthe precious metal bar, and receiving a thickness value of the preciousmetal coin or the precious metal bar. The method further includesperforming a measurement through a bulk of the precious metal coin orthe precious metal bar, and calculating a bulk property of the preciousmetal coin or the precious metal bar based on the measurement. Themethod further includes comparing the bulk property to a test propertybased on the surface resistivity value and the thickness value todetermine one of agreement or disagreement therewith, and providinginformation concerning verification of authenticity of the preciousmetal coin or the precious metal bar based on the agreement ordisagreement between the bulk property and the test property.

The term bulk electrical property is intended to be an electricalproperty that involves more than a surface electrical property of aprecious metal coin or precious metal bar. For example, the bulkelectrical property can be, but is not limited to, electric resistancethat would occur for a current passing from one point on the surface ofthe precious metal coin or precious metal bar, to another point on adifferent surface of the precious metal coin or precious metal bar. Forexample, the resistance for a current to flow from a point on theobverse of the precious metal coin to a point on the reverse of theprecious metal coin. Similarly, top surface and bottom surface for aprecious metal bar, etc.

A surface electrical property is, for example, an electrical resistivityof a precious metal coin or precious metal bar down to some depthgenerally referred to as the “skin depth” in the electrical arts. Theskin depth can be roughly a millimeter to a few or several millimeters,for example.

According to some embodiments, the bulk property is a bulk resistivityof the precious metal coin or the precious metal bar. According to someembodiments, providing information concerning verification ofauthenticity of the precious metal coin or the precious metal barcomprises displaying the information concerning verification via anon-numerical display.

A detection system according to some embodiments of the invention isshown in FIG. 2. The detection system 200 includes a housing 202 thathouses many of the components, including the first electrical coil. Thehousing 202 also acts as a sample support that supports the sample. Thetarget area 204 indicates the target position of the sample over thefirst electrical coil. The detection system 200 also includes a support206 that supports the second electrical coil 208 such that it is spacedapart from the first electrical coil by a known distance.

The detection system 200 according to some embodiments includes a weightmeasurement component 210 that is integrated into the platform on whichthe sample is placed. The weight measurement component 210 may determinethe weight of the sample and may communicate the weight to the dataprocessor for verifying the authenticity of the sample.

As shown in FIG. 2, the detection system 200 according to someembodiments includes a display device 212 and an input device 214. Thedisplay device may also be referred to herein as an “output display.”The input device 214 may be a keypad or other data entry means. Theinput device may also be referred to herein as a “user input system.”

FIG. 3 shows a cross-section of the detection system 200 shown in FIG.2. The detection system 300 includes a weight sensor platform 302 and aweight sensor load cell 304. The detection system 300 also includes thesupport 306 supporting the second electrical coil 308. The support 306is connected to the weight cell to maintain constant distance betweenthe second electrical coil 308 and the first electrical coil. The space310 for the first electrical coil to be disposed inside the housing 312is also shown.

A number of components are disposed inside the housing 312. These caninclude multiple frequency sine wave generators, a synchronous detector,an analog-to-digital converter, and a data processor such as amicroprocessor or computer, for example. FIG. 6 shows an overview of thesystem architecture, and FIG. 7 shows the analog circuits in moredetail. The analog-to-digital converter and the synchronous detector mayform at least part of the sensor system 108 shown in FIGS. 1B-1D. Thesine wave generators may provide a known alternating current or a knownalternating voltage. The data processor can be a dedicated “hard-wired”device, or it can be a programmable device. The data processor may be incommunication with a memory or data storage device. The memory may storea program to be executed by the data processor for determining theauthenticity of the sample. The memory can also store a metal databasewith specific gravity and resistivity information, as well as othertypes of information for a given metal or type of sample. Theinformation in the metal database may be directed to a variety ofdifferent metals, and/or may be specific to known types of coin andbullion.

According to some embodiments of the invention, the detection deviceincludes an adjustable support that separates the first coil from thesecond coil by a distance that can be adjusted. For example, whenmeasuring large bars, the first and second coils must be separatedsufficiently far apart that the bar can fit between them. However,because the electrical signal diminishes as the 4th power of thedistance between the coil, it can be beneficial to separate the twocoils by the minimum amount necessary to place the sample between them.Thus, an adjustable support can be used to separate the coils by adesirable distance. The adjustable support may have an encoder, forexample, a linear encoder, that provides a high-sensitivity measurementof the distance between the two coils. This distance can also beobtained during a calibration process, but having an encoder monitor theseparation distance can eliminate the need for determining theseparation distance by calibration. The two coils and adjustable supportmay be electrically connected but physically separated from the rest ofthe device, for example, by having wires that connect the coils andadjustable support to the device. The two coils and adjustable supportcan then be easily manipulated and positioned to measure a large bar,without having to move or manipulate the bar.

The detection device may also include a scale or length measuring aid.For example, measurement lines similar to those on a ruler may beprinted on the upper surface of the platform on which the sample isplaced. A user may use the lines to determine the length, width, ordiameter of a sample. The user may then enter this information into theinput device, and the data processor may use the input information todetermine the validity of the sample.

Alternatively, the data processor may display an expected sample length,width, or diameter, and the user may use the length measurement toconfirm that the sample has the expected dimensions. If the sample doesnot have the expected dimensions, this may be an indication that thesample is not valid. According to some embodiments, the data processormay calculate an expected area of the sample, and then the userinterface may indicate an expected length to which the user can comparethe actual sample.

FIG. 4A shows an embodiment in which the user interface indicates theexpected diameter of the sample. An indicator light 400 indicates afirst line 402. A display screen 404 indicates a second line 406, aswell as a shaded region on either side of the second line 406. The useraligns one edge of the coin with the first line 402, and the oppositeedge of the coin with the second line 406. If the second edge fallswithin the shaded region surrounding the second line 406, then coin isdetermined to have the expected area.

FIG. 4B shows an embodiment in which the user interface indicates theexpected length and width of the sample. An indicator light 408indicates a first line 410. The data processor then calculates expectedpositions of third and fourth edges of the sample based on theassumption that a first edge of the sample is aligned with the firstline 410, and a second edge of the sample is aligned with a second line412. The display device 404 shows a third line 414 and a fourth line 416that correspond to the expected area. The user aligns first and secondedges of the sample with the first and second lines 410, 412. The userthen uses the user interface to adjust the position of the third line414 or the fourth line 416. For example, the user may adjust the thirdline 414 to correspond to the position of the third edge of the sample.In the example shown in FIG. 4B, the user moves the third line 414upwards, and the motion of the third line 414 is reflected on thedisplay device. As third line 414 moves upwards, the data processorcalculates a new position of the fourth line 416 that corresponds to theexpected area, and the display device 404 updates the position of thefourth line 416. In the example shown in FIG. 4B, as the user moves thethird line 414 upwards, the fourth line 416 moves to the left. The usercontinues adjusting the position of the third line until it correspondsto the third edge of the sample. The user then examines the fourth edgeof the sample to determine whether it is above the fourth line, or fallswithin the acceptable margin of error indicated by the shaded regions oneither side of the fourth line 416. If the fourth edge does not fallwithin the shaded region, then the sample is not authentic.

According to some embodiments, a user controls the detection deviceusing the data processor, the display device, and the input device. Theuser enters the expected metal or sample by looking it up in a metaldatabase. The metal database may be saved in the memory, and a portionof the entries in the metal database may be displayed on the displaydevice. The user may use the input device to scroll through the metaldatabase and select a metal or sample.

The user can then weigh the sample and enter the weight using the inputdevice, or can use the built-in weight sensor, which may be incommunication with the data processor. The user then places the sampleon the target area. In FIG. 2, the target area 204 is indicated by acircle. The sample may be placed on top of this circle. The dataprocessor is connected to the AC power supply in such a way as it canspecify the frequency and amplitude of the output signal. The outputsignal may be a sine wave, for example.

Reference is now made to FIG. 1C. The signal generated by the signalgenerator 102 is applied to the first electrical coil 110, and thecurrent through the first electrical coil 110 is measured using thesecond sensor circuit 118. The sensor system 108 may include ananalog-to-digital converter. The second electrical coil 112 is supportedsuch that it faces the first electrical coil 110, and such that the twoelectrical coils 110, 112 are separated by a known distance.

While the first electrical coil 110 may be shown and referred to hereinas being position below the second electrical coil 112, the embodimentsof the invention are not limited to this configured. According to someembodiments, the first electrical coil 110 is positioned above thesecond electrical coil 112. The first electrical coil may be referred toherein as the “main coil.” The second electrical coil may be referred toherein as the “secondary coil.”

The second electrical coil 112 is connected through the sensor circuit114 to the data processor 116. When the signal is applied to the firstelectrical coil 110, the voltage appearing on the second electrical coil112 is measured by the sensor circuit 114. Both the current passingthrough the first electrical coil 110 and the voltage induced in thesecond electrical coil 112 are synchronously detected with thesynchronous detector. Real and imaginary parts of the current for thefirst electrical coil 110 and the voltage of the second electrical coil112 are measured. The data processor 116 uses the current detected inthe first electrical coil 110 to determine the resistivity of the sampleand the distance from the lower surface of the sample to the firstelectrical coil 110.

The data processor 116 may display the resistivity using the displaydevice, or may compare the resistivity to an expected resistivity basedon the metal or sample that the user selected from the database. In thiscase, the display device may display an indication of validity. Forexample, if the measured resistivity falls within a predetermined errorrange of the expected resistivity, the display device may indicate thatthe resistivity matches the expected resistivity. The display device mayindicate a percent deviation from the expected resistivity. If themeasured resistivity does not fall within the predetermined error rangeof the expected resistivity, the display device may indicate that thesample is likely fake or altered.

The data processor 116 uses the measured voltage induced in the secondelectrical coil 112 by the voltage applied to the first electrical coil110 to determine a quantity referred to herein as “electricalthickness.” The data processor 116 compares the electrical thickness tothe physical thickness of the sample as part of the validation process.

A sine wave voltage generated by the signal generator 102 is applied tothe second electrical coil 112, and the current passing through thesecond electrical coil 112 is measured by the third sensor circuit 120.The data processor 116 determines the distance from the upper surface ofthe sample to the second electrical coil 112 based on the measuredcurrent passing through the second electrical coil 112. The dataprocessor then determines the thickness of the sample based on thedetermined distance from the lower surface of the sample to the firstelectrical coil 110, the determined distance from the upper surface ofthe sample to the second electrical coil 112, and the known distancebetween the first electrical coil 110 and the second electrical coil112.

The display device may display the thickness, and may indicate theexpected dimensions of the sample, such as length, width, or diameter.The user can use the scale shown on the device platform to check whetherthe sample has the expected dimensions. According to some embodiments,the user uses the display device and the input device to enter themeasured dimensions. The data processor 116 calculates the specificgravity and reports the resistivity, specific gravity, and weight of thesample, and shows in a simple way on the display device whether thesample meets the criteria of a valid PM sample.

According to some embodiments of the invention, the display providesnumeric and non-numeric information for validating the sample. Forexample, as shown in FIG. 5, the output display may provide an expectedrange of values for the surface electrical property, referred to as the“Verifier Reading” in FIG. 5. A green region 500 may indicate anexpected range of values for a particular sample. A yellow region 502 oneither side of the green region may indicate values that are notoptimal, but may be acceptable, depending on whether the othermeasurements for the sample fall within acceptable ranges. A red region504 on either side of the yellow region indicates values that are notacceptable. If the sample reading falls within the red region 504, thesample is likely fake or altered.

The display may provide similar green, yellow, and red regions for thebulk electrical property, referred to in FIG. 5 as the “Thru-SampleReading.” An arrow 506 indicates where the measured value for the samplefalls within the green, yellow, and red regions. In FIG. 5, the measuredvalue for the surface and bulk electrical properties fall within thegreen regions. The display may also show a numerical value for thesurface and bulk electrical properties. The display may also show one ormore of a diameter, an area, a thickness, a precious metal weight, and atotal weight of the sample. The thickness may be measured by the deviceusing the methods described herein. The display may also show theexpected metal, which may be selected by the user prior to performingmeasurements on the sample. The display may also indicate the amount ofcharge remaining in the device's battery.

Validation Process

The first electrical coil 110 and the signal generator 102 incombination with the sensor system 108 and data processor 116 measurethe resistivity of the surface of the sample and the distance from firstelectrical coil 110 to the lower surface of the sample. These componentsin combination with the second electrical coil 112 are used to find afrequency at which the current through the first electrical coil 110 andthe voltage induced in the second electrical coil 112 have apredetermined phase difference. According to some embodiments, thisphase difference is 45 degrees, though the embodiments of the inventionare not limited to this value. The frequency at which the phasedifference is 45 degrees is proportional to the metal resistivitydivided by the “electrical thickness,” a quantity that is discussed inmore detail below.

The second electrical coil 112 in combination with the third sensorcircuit 120 and the data processor 116 measures the distance from thesecond electrical coil 112 to the upper surface of the sample. The dataprocessor 116 uses the two measured distances to calculate thethickness, or height, of the sample. The distance between the firstelectrical coil 110 and the second electrical coil 112 is known, so thethickness of the sample=distance between coils−distance from firstelectrical coil 110−distance from second electrical coil 112. This valueis referred to herein as the “mechanical thickness” or the “thicknessvalue.”

The data processor uses the measured value of the current through thefirst electrical coil 110 to determine the resistivity of the sample.The algorithm for computing the resistivity is described in more detailbelow.

The data processor 116 divides the determined resistivity by thefrequency at which the current through the first electrical coil 110 andthe voltage induced in the second electrical coil 112 have thepredetermined phase difference. This quotient is referred to herein as“electrical thickness.” In this way, the mechanical thickness andelectrical thickness are determined. In order for the sample to have thecorrect resistivity through its bulk, the electrical thickness mustequal the mechanical thickness.

A built-in weight scale or a separate weight scale is used to measurethe weight of the sample. The data processor 116 uses the measuredweight in combination with the mechanical thickness to determine thearea of the sample, which is either π×radius² in the case of a roundcoin or length×width in the case of the rectangular bar. Virtually allPM samples are in one of these two forms, and the radius, length andwidth are easy to measure by conventional means. Note that the weightscale can be used or not at the discretion of the user, where the usercan enter the known total weight, or the PM weight, instead of having itmeasured. In some cases it is not easy to measure the weight of asample, for example, when it is mounted in a hard plastic case.According to some embodiments, the detection system does not include aweight sensor, since most users already have a scale and can easilyenter the weight.

According to some embodiments, the user measures the diameter in thecase of a coin, or the length and width in the case of a bar, using thescale provided on the upper surface of the device, or by measurementwith another measurement device such as a pair of calipers, for example.The user then enters this information using the user interface. The dataprocessor 116 uses the dimensions entered, in combination with themechanical thickness and the weight, to calculate the specific gravity.The data processor may display the resistivity, the weight, the specificgravity, and the thickness, on the display device. These values all mustagree with those of the expected metal element or alloy. If they do notagree, then the PM sample is altered or fake.

The sample target indicates to the user where to place the sample to betested. The input device in combination with the display device allowsthe user to enter the coin type, the bar type, or the metal alloy, andthe database contains the specific gravity and resistivity of the metal.These values are used in the calculation of the specific gravity and theelectrical thickness of the sample.

The data processor 116 determines the authenticity of the sample usingthe algorithms described here and displays an indication of theauthenticity of the sample using the display device. The PM sample isonly valid if 1) the electrical thickness equals the mechanicalthickness, 2) the resistivity of the sample metal agrees with that ofthe selected metal or alloy, and 3) the weight in combination with thevolume calculates to the correct specific gravity.

How to Make the System

According to some embodiments of the invention, a circuit board holdsand connects the data processor 116, the sensor system 108 including ananalog-to-digital converter and a synchronous detector, the inputdevice, the display device, the AC power supply, and a memory containinga program for execution and a metal database. The circuit board holds orconnects to the weight sensor (if included), the first electrical coil110, and the second electrical coil 112. The display device and inputdevice are conveniently placed for the user on the housing, as is thetarget area. The synchronous detector can be a hardware detector, orperformed in software or in a field-programmable gate array asmultipliers.

According to some embodiments, the detection system is connected to anexternal weight scale and reads the weight from that scale.

A length scale can be included on the detection system, for example, aspart of the housing or printed in a convenient place. Alternatively, theuser can measure the dimensions of the sample with calipers or a ruler.Alternatively, an electronic method for measuring distance can bebuilt-in, for example a wire with a capstan could deploy a measuringwire to measure the sample's diameter or length and width.

The data processor according to some embodiments is a microprocessor.The microprocessor may be a PC or tablet, connected by a conventionalinterface such as USB or Bluetooth, and also have the keypad anddisplay. According to some embodiments, the housing includes themeasurement components but not the display device or input device. Inthis case, all the inputs and displays can be done by a conventionalcomputer or pad.

The first electrical coil 110 and second electrical coil 112 can beessentially the same and their functions can be interchanged. Also,other measurement modes can be used. For example, the resistivity of thesurface of the sample can be measured for a quick check, and the usercan control whether the complete measurement, such as thickness andspecific gravity, is performed. If the surface resistivity is wrong, theother measurements are unnecessary to determine if the sample is alteredor fake, and therefore the verification process may be terminated.

The system according to some embodiments may include two or more pairsof coils. FIGS. 4A and 4B shows an example that includes two pairs ofcoils. In FIG. 4A, upper coil 418 and its corresponding lower coil (notshown) have a larger area than upper coil 420 and its corresponding pair(no shown). The pair of smaller coils may be spaced closer together thanthe pair of larger coils, as shown in FIG. 4A. The larger coils may beused to examine samples that are thicker or have a larger surface area.The smaller coils may be used to examine thinner samples, or sampleswith a smaller surface area. Each pair may connect to the sensor systemsuch that the measurements described herein may be performed usingeither pair of electrical coils. An LED 422 may indicate that the largerpair of electrical coils is in use, while a second LED 424 may indicatethat the smaller pair of electrical coils is in use. The user may selectthe appropriate pair of electrical coils for a given sample using theuser interface. The system will then perform measurements on the sampleusing the selected pair of electrical coils.

Using the Detection System

Described herein is an example in which a user tests the validity of a 1oz. gold coil using the detection system. The user selects pure goldfrom the database, and the data processor retrieves the specific gravityfor pure gold, 19.4 grams per CC, and the resistivity for pure gold, 2.2micro Ohm cm.

The system uses the built-in scale to weigh the sample, and it weighs31.14 grams. Alternatively, an external scale is used to weigh tosample, and the weight is communicated to the data processor directlyfrom the external scale, for example using a wired or wirelesscommunication system, or the user inputs the weight using the inputdevice. The detection system then determines the resistivity of thebottom surface of the sample, which in this example is 2.2 micro Ohm Cm.Thus, the sample's resistivity matches the resistivity for pure goldthat was pulled from the database.

The detection system determines the mechanical thickness using thebottom and top coils to measure the distance to the top and bottomsurfaces, respectively, and subtracting the distance between the coils.The data processor determines that the mechanical thickness is 2.62 mm.Then the system measures the electrical thickness by a generating lowfrequency voltage at the bottom coil reading the voltage at the topcoil, and adjusting the sine frequency until the phase angle between thecurrent in the lower coil and the voltage in the upper coil is 45degrees. Using this frequency, it calculates the electrical thickness,and gets 2.62 mm. The terms “lower coil” and “upper coil” may refer tothe first electrical coil and second electrical coil, respectively, orto the second electrical coil and first electrical coil, respectively.The roles of the first and second electrical coils are interchangeable,and are independent of the orientation (i.e., above or below) of oneelectrical coil with respect to the other electrical coil. Further, thetwo coils are not required to be stacked vertically, but could assumealternative orientations as long as the two coils are opposite oneanother and separated by a distance.

Using the weight and the mechanical thickness, and the database valuefor specific gravity, the user is advised of the expected diameter ofthe coin, 30.0 mm. The user moves the coin to the measuring scale andreads the diameter, which is 30.0 mm. Alternatively, the user interfacemy indicate the expected diameter on the display screen, as describedabove, and the user may place the coin on the surface of the device tocompare the coin's diameter to the expected diameter.

In this way the surface resistivity, the bulk resistivity, the thicknessand diameter, and the specific gravity are all checked and must agreewith the gold values from the metal database. The agreement doesn't haveto be perfect. Typically agreement within 5% for resistivity, agreementwithin 5% between electrical and mechanical thickness, and agreementwithin 7% for diameter are sufficient to prove that the coin is valid,or in this example, that it is made from pure gold. The user interfacemay indicate a % error, and may also non-numerically indicate whetherthe % error for a given sample is acceptable.

If the “pure gold” coin were in fact made from tungsten which has beengold plated, then the surface resistivity would be wrong. The weight,thickness, diameter, and specific gravity could all be in agreement withthe expected values, but the lack of agreement of the surfaceresistivity would enable the detection system to determine that thesample is not valid.

If the “pure gold” coin were made from a copper alloy that has the sameresistivity as gold, then the surface resistivity would be in agreementwith the resistivity retrieved from the metal database, and themechanical and electrical thicknesses would also agree. However, thespecific gravity would not match the specific gravity stored in themetal database, and the data processor would determine that the samplewas invalid.

If the “pure gold” coin were made from heavily gold clad tungsten, thenthe surface resistivity may match the value in the metal database, andthe weight and specific gravity could be as expected. However, themechanical and electrical thickness would not be equal because the pieceof tungsten in the middle of the coin would have the wrong resistance,and the electrical thickness would not agree with the mechanicalthickness. Thus, the data processor would determine that the sample wasnot a pure gold coin.

For all precious metals and their alloys, one of the conditionsdescribed above would fail to be met if the material were altered orfake.

The embodiments of the invention are not limited to ascertaining thevalidity of a precious metal sample. The system and methods could beused to test other metals and alloys for their correct composition, orto identify the metal or alloy.

Measurement Procedure

A typical measurement procedure according to some embodiments of theinvention is described below. While the steps are described in aparticular order, the embodiments of the invention are not limited tothis order. One skilled in the art will appreciate how the steps can beperformed in an alternative order to gather the necessary informationfor the data processor to make a determination of validity. Further, thematerials and values described below are purely exemplary and areintended to elucidate the system and methods described herein in anon-limiting manner.

According to some embodiments, the user begins the measurement processby entering information about the sample using the input device. Thesample information may include a metal type or coin type, for example,“22 k gold,” or “Krugerrand.” The user may also enter the expectedweight (W_(e)) of the sample.

The data processor then retrieves information from the metal databasebased on the information provided by the user. According to someembodiments, the data processor extracts the following values from themetal database: specific gravity (G_(e)), resistance (R_(e)), andthickness (T_(e)) if a specific coin or bar is selected. The subscript“e” is used herein to indicate that these are expected values, asopposed to values based on measurements of the sample. Temperaturecoefficients, resistance range, and other minor adjustments can also beretrieved from the metal database.

The system then calibrates the first and second electrical coils. Thisis done without a sample placed between the coils. The data processorapplies a voltage to the first electrical coil using the AC powersupply, and the sensor system measures the real Re and imaginary Imparts of the current I_(1c) passing through the first electrical coil.FIG. 8 illustrates the structure of a field-programmable gate array(FPGA) according to some embodiments that is used to measure the realand imaginary parts of detected signals. The data processor uses thereal and imaginary parts of the current to calculate the calibrationinductance Lie and the calibration resistance R_(1c) of the firstelectrical coil at frequency f:

L _(1c)=1/(2 Pi f Im(I _(1c)))   (1)

R _(1c)=1/Re(I _(1c))   (2)

This process also occurs for the second electrical coil, giving L_(2c)and R_(2c).

The data processor then instructs the user to place the sample on thetarget area between the first electrical coil and the second electricalcoil. The data processor applies a voltage to the first electrical coilusing the AC power supply, and the sensor system measures the real Reand imaginary Im parts of the current I_(1s) passing through the firstelectrical coil when the sample is present. The system then calculatesthe inductance L_(1s) and resistance R_(1s) of the first electrical coilwhen the sample is present:

L _(1s)=1/(2 Pi f Im(I _(1s)))   (3)

R _(1s)=1/Re(I _(1s))   (4)

The data processor then uses the calibration inductance L_(1c) andresistance R_(1c) and the sample inductance L_(1s) and resistance R_(1s)to calculate two values referred to herein as “Q” and “k” for firstelectrical coil:

k ₁=1−L _(s1) /L _(c1)   (5)

Q ₁=(L _(c1) −L _(s1))/(R _(c1) −R _(s1))   (6)

The data processor then calculates the sample resistance r_(s):

r _(s)=α Q₁̂2   (7)

where α is a constant based on the sensor and the frequency.

The data processor also calculates the distance Dis from the firstelectrical coil to the sample:

D _(1s)=function(k ₁)   (8)

where the function is a Pade or other curve fit to a measuredrelationship between k and D_(1s).

In order to calculate the distance D_(2s) from the second electricalcoil to the sample, the data processor applies a voltage to the secondelectrical coil when the sample is present using the AC power supply,and the sensor system measures the real Re and imaginary Im parts of thecurrent I_(2s) passing through the second electrical coil when thesample is present. The data processor then calculates the inductanceL_(2s) of the second electrical coil when the sample is present usingequation (3), and calculates k₂ using equation (5). The distance D_(2s)from the second electrical coil to the sample is determined to be

D _(2s)=function(k ₂)   (9)

where the function is a Pade or other curve fit to a measuredrelationship between k₂ and D_(2s).

The data processor then calculates the mechanical thickness T_(m) of thesample:

T _(m) =D ₁₂ −D _(1s) −D _(2s)   (10)

where D₁₂ is the distance between the first electrical coil and thesecond electrical coil. The process is illustrated schematically in FIG.9. Alternatively, the data processor may receive a value for themechanical thickness. For example, the user may measure the thicknessand enter the thickness value using a user interface. The data processormay use the received thickness value for the calculations below insteadof performing the steps outlined above to calculate the thickness.

The system then obtains the weight W_(s) of the sample, either using abuilt-in or external yet integrated weight sensor (for example, one thatis wired or wirelessly connected to the system), or prompts the user toenter the weight of the sample if the system does not have an integratedscale.

Next, the system measures the electrical thickness T_(e) of the sample.FIG. 10 illustrates schematically the system and process for measuringthe electrical thickness according to some embodiments. The dataprocessor uses the AC power supply to drive the first electrical coil.The sensor system measures the current in the first electrical coil andthe voltage induced in the second electrical coil. The sensor systemreads the phase angle φ between the current I_(1s) in the firstelectrical coil and the voltage V_(2s) in the second electrical coilwhen the sample is present:

$\begin{matrix}{\phi = {{\tan^{- 1}\frac{{Im}\left( I_{1S} \right)}{{Re}\left( I_{1S} \right)}} - {\tan^{- 1}\frac{{Im}\left( V_{2S} \right)}{{Re}\left( V_{2S} \right)}}}} & (11)\end{matrix}$

The data processor instructs the AC power supply to adjust the frequencyof the voltage applied to the first electrical coil until φ has apredetermined value, for example, −45 degrees. This can be done by aniterative search procedure using Newton's method, or by other methods.This is a hardware measurement; the frequency is adjusted until thecorrect frequency is generated. The frequency at which φ becomes −45degrees is F₄₅.

The thickness is a function of r_(s) and F₄₅. The resistance r_(s) wasobtained using equation (7). The electrical thickness T_(e) iscalculated as

T _(e) =γr _(s) /F ₄₅   (12)

where γ is a constant for the sensor, adjusted slightly for any distanceD_(1s) corrections that are necessary. The electrical thickness T_(e)can be calculated based on F₄₅ using equation (12), and reported to theuser as a numerical value and/or as an arrow indicating a position in arange of expected values, as shown in FIG. 5. Alternatively oradditionally, the device may calculate a frequency for which φ isexpected to be −45 degrees. The sensor system may apply this frequencyand measure the angle φ. The arctangent of φ should be 1 if thefrequency F₄₅ is exactly as expected (arctan (45 degrees)=1). The devicemay display the bulk measurement result to the user as a % error in thisangle arctangent. For example, arctan (43.5 degrees)=0.95, so thisrepresents a 5% error in the expected frequency. The display may showgreen, yellow, and red regions of the bulk reading to correspond tocertain % error in this frequency. This method only requires one bulkfrequency measurement to get a result, as opposed to performing multiplemeasurements to determine F₄₅.

Next, the data processor calculates the area A_(s) of the sample basedon the mechanical thickness T_(m), the weight W_(s), and the specificgravity G_(s) retrieved from the metal database:

A _(s) =W _(s)/(G _(s) T _(m))   (13)

If the sample is a coin, the data processor calculates the expectedradius:

Radius=(Area/π)̂(½)   (14)

If the user selected a metal type and not a coin, then the user measuresthe radius or length and width of the sample, and the data processordetermines whether the radius or length and width measured by the useragrees with the area calculated based on the weight W_(s), specificgravity G_(s), and mechanical thickness T_(m).

Finally, the data processor generates a report to the user that isdisplayed using the display device. The following criteria must be metfor the sample to be authentic:

-   1) The sample resistance r_(s) must match the value r_(e) in the    metal database for the coin or bullion (typically within +−3%).-   2) The mechanical thickness T_(m) must match the electrical    thickness T_(e) (T_(m)=T_(e) typically within +−5%).-   3) The weight W_(s) must match the expected weight W_(e) for the    coin or bullion (typically within +−0.1%).-   4) The mechanical thickness T_(m) must agree with that of the    selected coin or bullion, or the measured dimensions must match the    calculated area (either the π×diameter or the length×width,    typically within 5%).

If these criteria are met, the sample must be the metal, alloy, or coinselected, and the display device indicates that the sample is authentic.If any of the criteria are not met, then the display device indicatesthat the sample is not authentic. The display device may also displaythe expected and calculated values related to the criteria, and mayindicate which criteria are or are not met.

From the perspective of the user, the procedure is actually simple. Theuser enters the coin, bullion, or metal type, and the expected weight ofeither the precious metal or the entire sample (for example, aKrugerrand has 31.11 grams of gold, but weighs 33.93 grams). The userhits a start button, places the sample on the target area, and then theresults are displayed on the display device. Readings that are outsidethe expected range may be displayed in red, marginal ones in yellow, andreadings within the expected range in green. This way, at a glance, theuser can see whether the sample is valid.

The embodiments illustrated and discussed in this specification areintended only to teach those skilled in the art how to make and use theinvention. In describing embodiments of the invention, specificterminology is employed for the sake of clarity. However, the inventionis not intended to be limited to the specific terminology so selected.The above-described embodiments of the invention may be modified orvaried, without departing from the invention, as appreciated by thoseskilled in the art in light of the above teachings. It is therefore tobe understood that, within the scope of the claims and theirequivalents, the invention may be practiced otherwise than asspecifically described.

1.-25. (canceled)
 26. A system for verifying authenticity of preciousmetal coins and bars, comprising: a sensor system defining a sampleregion configured to receive a precious metal coin or a precious metalbar therein, said sensor system comprising: a first electrical coil; asecond electrical coil spaced apart from said first electrical coil withsaid sample region therebetween; and an adjustable support configured toseparate said first electrical coil from said second electrical coil bya distance that can be adjusted by a user; a sample support arranged tosupport said precious metal coin or said precious metal bar in saidsample region; a data processor configured to communicate with saidsensor system so as to receive a detection signal therefrom and toprovide an output signal; a data storage device configured tocommunicate with said data processor, said data storage deviceconfigured to store at least some physical properties corresponding to aprecious metal of interest; and an output display configured tocommunicate with said data processor to receive said output signal andto display information based on said output signal, wherein said sensorsystem is configured to detect a bulk electrical property of saidprecious metal coin or said precious metal bar, said bulk electricalproperty being a property measured from a first surface of said preciousmetal coin or said precious metal bar to a second surface of saidprecious metal coin or said precious metal bar opposing said firstsurface, wherein said data processor is configured to process saiddetection signal from said sensor system and to retrieve a storedphysical property corresponding to a precious metal from said datastorage device to provide said output signal such that said outputsignal includes a measured value of said bulk electrical property and acorresponding range of expected values of said bulk electrical property,and wherein said output display uses said output signal to displayinformation based on said measured value of said bulk electricalproperty and said corresponding range of expected values of said bulkelectrical property for said user to be able to make an authenticityverification of said precious metal coin or said precious metal bar. 27.The system for verifying authenticity of precious metal coins and barsaccording to claim 26, further comprising: a signal generator, whereinsaid sensor system further comprises: a sensor circuit selectivelyconnecting said signal generator to said first and second electricalcoils, said sensor circuit being configured to provide a measurement ofa current in said first electrical coil and a measurement of a voltageinduced in said second electrical coil, and wherein said data processoris configured to process said measurement of said current in said firstelectrical coil and said measurement of said voltage induced in saidsecond electrical coil and to retrieve said stored physical propertycorresponding to said precious metal from said data storage device toprovide said output signal such that said output signal includes saidmeasured value of said bulk electrical property and said correspondingrange of expected values of said bulk electrical property.
 28. Thesystem for verifying authenticity of precious metal coins and barsaccording to claim 27, wherein said data processor is configured toprovide said output signal based on a phase shift between saidmeasurement of said current and said measurement of said voltage. 29.The system for verifying authenticity of precious metal coins and barsaccording to claim 27, wherein said bulk electrical property is a bulkresistivity of said precious metal coin or said precious metal bar. 30.The system for verifying authenticity of precious metal coins and barsaccording to claim 27, wherein said data processor is configured tocontrol said signal generator to adjust a frequency of a voltage appliedto said first electrical coil such that a phase shift between saidmeasurement of said current and said measurement of said voltage has apredetermined value; and wherein said data processor is configured toprovide said output signal based on said frequency at which said phaseshift has said predetermined value.
 31. The system for verifyingauthenticity of precious metal coins and bars according to according toclaim 26, further comprising: a signal generator, wherein said sensorsystem further comprises: a sensor circuit selectively connecting saidsignal generator to said first electrical coil to provide a measurementof a current in said first electrical coil, wherein said data processoris configured to process said measurement of said current in said firstelectrical coil and to retrieve a stored physical property correspondingto a precious metal from said data storage device to provide said outputsignal such that said output signal includes a measured value of asurface electrical property and a corresponding range of expected valuesof said surface electrical property, and wherein said output display isconfigured to use said output signal to display information based onsaid measured value of said surface electrical property and saidcorresponding range of expected values of said surface electricalproperty for said user to be able to make an authenticity verificationof said precious metal coin or said precious metal bar.
 32. The systemfor verifying authenticity of precious metal coins and bars according toclaim 31, wherein said sensor system further comprises a third sensorcircuit selectively connecting said signal generator to said secondelectrical coil to provide a measurement of a current in said secondelectrical coil, wherein said data processor is configured to processsaid measurement of said current in said second electrical coil toprovide said output signal such that said output signal includes ameasured value of a thickness value of said precious metal coin or saidprecious metal bar.
 33. The system for verifying authenticity ofprecious metal coins and bars according to claim 32, wherein saidadjustable support further comprises an encoder in communication withsaid data processor, said encoder being configured to provide ameasurement of a distance between said first electrical coil and saidsecond electrical coil to said data processor, wherein said dataprocessor is further configured to process said measurement of saiddistance to provide said output signal such that said output signalincludes said measured value of said thickness value of said preciousmetal coin or said precious metal bar.
 34. The system for verifyingauthenticity of precious metal coins and bars according to claim 26,further comprising: a signal generator, wherein said sensor systemfurther comprises: a first sensor circuit selectively connecting saidsignal generator to said first electrical coil, said first sensorcircuit being configured to provide a measurement of a current in saidfirst electrical coil, and a second sensor circuit selectivelyconnecting said signal generator to said second electrical coil, saidsecond sensor circuit being configured to provide a measurement of acurrent in said second electrical coil; and wherein said data processoris configured to process said measurement of said current in said firstelectrical coil and said measurement of said current in said secondelectrical coil to provide said output signal such that said outputsignal includes at least a measured value of a thickness value of saidprecious metal coin or said precious metal bar, and wherein said outputdisplay is configured to use said output signal to display informationbased on said thickness value of said precious metal coin or saidprecious metal bar for said user to be able to make an authenticityverification of said precious metal coin or said precious metal bar. 35.The system for verifying authenticity of precious metal coins and barsaccording to claim 34, wherein said data processor is further configuredto retrieve a specific gravity value corresponding to a precious metalfrom said data storage device and receive a weight value correspondingto said precious metal coin or said precious metal bar, and to providesaid output signal such that said output signal further includes anexpected diameter of said precious metal coin or an expected area ofsaid precious metal bar.
 36. The system for verifying authenticity ofprecious metal coins and bars according to claim 35, wherein saidadjustable support further comprises an encoder in communication withsaid data processor, said encoder being configured to provide ameasurement of a distance between said first electrical coil and saidsecond electrical coil to said data processor, wherein said dataprocessor is further configured to: process said measurement of saidcurrent through said first electrical coil to determine a first distancebetween said first electrical coil and said precious metal coin or saidprecious metal bar; process said measurement of said current throughsaid second electrical coil to determine a second distance between saidsecond electrical coil and said precious metal coin or said preciousmetal bar; and provide said output signal such that said output signalincludes at least said measured value of said thickness value of saidprecious metal coin or said precious metal bar based on said firstdistance, said second distance, and said distance provided by saidencoder.
 37. The system for verifying authenticity of precious metalcoins and bars according to claim 36, wherein said data processor isconfigured to calculate an expected area of said precious metal coin orsaid precious metal bar based on said thickness value, said specificgravity value, and said weight value, and wherein said output displayprovides a non-numerical indication of said expected area and anacceptable error range to allow said user to compare said expected areato an actual area of said precious metal coin or said precious metalbar.
 38. The system for verifying authenticity of precious metal coinsand bars according to claim 26, wherein said adjustable support furthercomprises an encoder in communication with said data processor, saidencoder being configured to provide a measurement of a distance betweensaid first electrical coil and said second electrical coil to said dataprocessor.
 39. The system for verifying authenticity of precious metalcoins and bars according to claim 26, further comprising a user inputsystem configured to communicate with said data storage device and saiddata processor, wherein said user input system allows said user toselect at least one of a precious metal type, alloy parameters, weight,or shape.
 40. The system for verifying authenticity of precious metalcoins and bars according to claim 26, further comprising a weightmeasurement component in communication with said data processor.
 41. Asystem for verifying authenticity of precious metal coins and barsaccording to claim 40, wherein said data processor is configured toreceive a weight value of said precious metal coin or said preciousmetal bar from said weight measurement component.
 42. A system forverifying authenticity of precious metal coins and bars, comprising: asensor system defining a sample region configured to receive a preciousmetal coin or a precious metal bar therein, said sensor systemcomprising: a first electrical coil; a second electrical coil spacedapart from said first electrical coil by a first distance with saidsample region therebetween; a third electrical coil; a fourth electricalcoil spaced apart from said third electrical coil by a second distancewith said sample region therebetween, said second distance beingdifferent from said first distance; a sample support arranged to supportsaid precious metal coin or said precious metal bar in said sampleregion; a user input system configured to allow a user to select saidfirst and second electrical coils or said third and fourth electricalcoils; a data processor configured to communicate with said sensorsystem and said user input system so as to receive a detection signaldetected by said first and second electrical coils or said third andfourth electrical coils based on said user's selection, and to providean output signal; a data storage device configured to communicate withsaid data processor, said data storage device configured to store atleast some physical properties corresponding to a precious metal ofinterest; and an output display configured to communicate with said dataprocessor to receive said output signal and to display information basedon said output signal, wherein said sensor system is configured todetect a bulk electrical property of said precious metal coin or saidprecious metal bar, said bulk electrical property being a propertymeasured from a first surface of said precious metal coin or saidprecious metal bar to a second surface of said precious metal coin orsaid precious metal bar opposing said first surface, wherein said dataprocessor is configured to process said detection signal from saidsensor system and to retrieve a stored physical property correspondingto a precious metal from said data storage device to provide said outputsignal such that said output signal includes a measured value of saidbulk electrical property and a corresponding range of expected values ofsaid bulk electrical property, and wherein said output display uses saidoutput signal to display information based on said measured value ofsaid bulk electrical property and said corresponding range of expectedvalues of said bulk electrical property for said user to be able to makean authenticity verification of said precious metal coin or saidprecious metal bar.
 43. A method for verifying authenticity of preciousmetal coins and bars using an electronic apparatus, comprising:inputting into said electronic apparatus information identifying atleast a type of a precious metal coin or a precious metal bar to beverified; selecting a distance between a pair of electrical coilsincluded in said electronic apparatus, said pair of electrical coilsbeing configured to receive a precious metal coin or said precious metalbar therebetween; performing a measurement of a bulk electrical propertyof said precious metal coin or said precious metal bar using said pairof electrical coils spaced apart by said selected distance, said bulkelectrical property being a property measured from a first surface ofsaid precious metal coin or said precious metal bar to a second surfaceof said precious metal coin or said precious metal bar opposing saidfirst surface; retrieving a stored bulk electrical property of saidprecious metal coin or said precious metal bar corresponding to saidmeasured bulk electrical property for said inputted type of saidprecious metal coin or said precious metal bar; and providinginformation from said electronic apparatus for verification ofauthenticity of said precious metal coin or said precious metal barbased on said measured bulk electrical property and said retrieved bulkelectrical property.
 44. The method for verifying authenticity ofprecious metal coins and bars using an electronic apparatus according toclaim 43, wherein selecting said distance between said pair ofelectrical coils comprises adjusting a distance between said pair ofelectrical coils using an adjustable support.
 45. The method forverifying authenticity of precious metal coins and bars using anelectronic apparatus according to claim 43, wherein said electronicapparatus comprises a first electrical coil and a second electrical coilspaced apart from said first electrical coil by a first distance, athird electrical coil, and a fourth electrical coil spaced apart fromsaid third electrical coil by a second distance, said second distancebeing different from said first distance, and wherein selecting saiddistance between said pair of electrical coils comprises selecting saidfirst and second electrical coils or said third and fourth electricalcoils.